- Friend classes are useful when a class wants to hide features from users which are needed only by another, tightly coupled class. 

- Implementation details can be kept safe by providing friend status to a tightly cohesive class.

WATER MARK is a divided segment of used and free blocks. Blocks which are below high WATER MARK i.e. used blocks, have at least once contained some data. This data might have been deleted later. Oracle knows that blocks beyond high WATER MARK don’t have data; it only reads blocks up to the high WATER MARK during a full table scan. 

Locking is a mechanism to ensure data integrity while allowing maximum concurrent access to data. It is used to implement concurrency control when multiple users access table to manipulate its data at the same time.

Advantages :

- Avoids deadlock conditions

- Avoids clashes in capturing the resources

A Peoplesoft database is expression which point out a database containing Peoplesoft objects. For Oracle and only for Oracle, Peoplesoft consists in 3 schemas namely:

- PS (PSDBOWNER table owner),

- PEOPLE (for connection checking) and

- SYSADM (by default), the last one contains all the objects/data.

One of the database objects is connected with single Oracle schema, and all processes that connect to the database use the standard PSFT login procedure. PSFT login is used because to refer to the collection of tables in the administrative schema within an Oracle database. Every process that makes a 2-tier connection to the database identifies itself with a PSFT user or operator ID. Hence the interaction goes.

Oracle Web Cache is a secure reverse proxy cache and a compression engine deployed between Browser and HTTP server, Browser and Content Management server to improve the performance of web sites by caching frequently accessed content. Oracle Web Cache supports:

- Static content caching

- Dynamic content caching

- Partial Page catching

- Request Filtering.

- Online backup is one which is taken at the time the database is running in the ARCHIVELOG mode.

- Following files should be backed up during the Offline Backup: All data file, all control file and all online redo log file. But in the case of the online backup following files is backed up: All data files all archived redo log files and one control file via the alter database command.

- Offline database we cannot rely upon but in case of online database no issues.

- Offline backup no archived mode is required but in the online backup it is must.

Oracle HTTP Server is managed by OPMN which stands for Oracle Process Manager and Notification Server. With the use of opmnctl utility we can start, stop and restart Oracle HTTP Server. If we don’t use this utility the configuration management infrastructure cannot detect or communicate with the Oracle HTTP Server processes, and problems may occur.

The startproc command for the case of Windows is: ORACLE_HOME\opmn\bin> opmnctl [verbose] startproc ias-component=HTTP_Server.

To stop Oracle HTTP Server, use the stopproc command: Windows: ORACLE_HOME\opmn\bin> opmnctl [verbose] stopproc ias-component=HTTP_Server.

Oracle HTTP Server is the Web server component of Oracle Database. It is based on the Apache HTTP Server. It is robust and reliable server due to following features:

- Provide high availability infrastructure integration with Oracle Process Manager and Notification Server (OPMN), for process management, death detection and failover for Oracle HTTP Server processes.

- Provide Dynamic Monitoring Services (DMS) metrics that give runtime performance statistics for Oracle HTTP Server processes.

- Enable securing of transactions with Secure Sockets Layer (SSL) technology.

- Execute Perl scripts in the same process as the Oracle HTTP Server, or as CGI script.